The present invention relates generally to aerodynamic surfaces and, more particularly, to improved constructions and control schemes for such surfaces that provide aerodynamic control and significant reduction of the negative effects of non-uniform flow over such surfaces.
Aerodynamically-driven oscillations (ADO) have long been recognized as one of the more serious problems facing the structural integrity and maintainability of aerospace vehicle components such as fixed wings and rotor blades. ADO can, when coupled with the natural frequencies of the component, result in resonance causing large deformations and, consequently, the rapid fatigue of the component. Component fatigue, in turn, results in a shorter life cycle and, in severe conditions, can cause failure of the component.
Aerodynamically-driven oscillations of structural components cause a phenomenon known as flutter. Flutter can occur over a wide range of operating conditions spanning the lower end of subsonic flow up to trasonic flow. In the absence of ADO, aerospace vehicle components are more tolerant to variations in their design, operating conditions and, more importantly, less susceptible to costly structural failures and repairs. Accordingly, flutter suppression technology is highly sought after by an aerospace community faced with escalating costs of component production and maintainability.
Among the known factors directly affecting the intensity of ADO are the magnitude and frequency parameters of unsteady aerodynamic forces (e.g., shed wakes or free stream gusts) to which the component is subjected. To suppress the onset of flutter, these forcing parameters can be affected using an active control technique. A common prior art device used for gust alleviation and the suppression of flutter is an active trailing edge aileron-like control surface. The oscillatory motion of the controller is desirably 180 degrees out of phase with the unsteady motion caused by the aerodynamic forcing. However, this control technique requires the use of a mechanical actuator and linkages to control the motion of the aileron-like surface. Further, aileron-like surfaces necessarily introduce aerodynamic surface discontinuities that undermine aerodynamic efficiencies and increase the radar cross-section signature of the aircraft.
Accordingly, what is needed in the art is a device that will suppress the onset of flutter in an aircraft component while minimizing or eliminating associated moving parts and discontinuities of the component surface.
According to principles of the present invention, an active control device is disclosed comprising an array of actively controlled oscillating air jets disposed on an aircraft structure. In a preferred embodiment, the device senses parameters associated with incipient unsteady aerodynamic excitation, such as free stream gusts, shed wakes in rotor and turbomachinery flows, or oscillatory motion of trailing edge control surfaces such as ailerons. These parameters are provided as input signals to a processor. Based on the input signals, the processor generates output signals that are used to operate the air jet array in a manner counteractive to the unsteady forcing. The air jet array can be used on numerous aircraft structures, including rotor blades, wings, engine inlets, engine exhausts, blunt surfaces and nozzles.